Power flow solutions of AC/DC micro-grid structures

This paper presents a new and general frame-of-reference for the unified, power flow solution of AC and DC micro-grids using the Newton-Raphson method, where the quadratic convergence towards the solution is preserved. The cornerstone of this modeling development in power flow theory is the so-called multi-terminal VSC-HVDC system. In this frame-of-reference, an AC micro-grid of arbitrary configuration is connected to the high-voltage side of the LTC transformer of a VSC station. In turn, the DC side of each VSC is linked to a DC system of arbitrary configuration. Any number of AC micro-grids may exist and the DC system may contain single load or generation points such as a PV installation. Each VSC model takes into account, in aggregated form, the phase-shifting and scaling nature of the PWM control. It also accounts for the VSC current design limits, PWM limits within the linear range, switching losses and ohmic losses.